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Transmission Line with SS 18W/8531G

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  • Transmission Line with SS 18W/8531G

    Looking to see if any body has done a T-Line with this woofer. I see Tony Gee did one with the 4 ohm version but that specs different. I may match it with a Vifa XT25 tweeter.

    Thanks

  • #2
    Re: Transmission Line with SS 18W/8531G

    What do you prefer? Tapered or ML? I have measurements from the one I have here. Do you have a link to the Gee version?
    Mongo only pawn in game of life
    ____
    Ed

    Comment


    • #3
      Re: Transmission Line with SS 18W/8531G

      Thanks Ed. I think Zaph's measurements would be good to use. Here they are.
      http://www.zaphaudio.com/6.5test/compare.html
      Lets try tapered.
      Opps you want Tony Gee's . Ok here it is.
      http://www.humblehomemadehifi.com/Optimo.html
      He was kind enough to send me Hi-res drawings of it today too. I could email that to you if you want.

      Comment


      • #4
        Re: Transmission Line with SS 18W/8531G

        The SS8531 models really well in a tapered or mass-loaded TL. An ML-TL will get you a bit lower F3 than an equivalent tapered TL having the same net line volume. I just happened to be modeling an ML-TL for this driver today (using Zaph's measurements) and have attached a system response graph for it. The 3-way system cabinet I modeled for this would have internal dimensions of 7.5"W x 7.5"D x 38"H, with the center of the 8531 located 13" below the (internal) top. The port's center is located 3.5" above the (internal) bottom. The port is 6" long and 2" in diameter. I used a stuffing density of 0.8 lb/cu.ft., requiring a total of ~9 ounces of stuffing in the top half of the cabinet. Now, if you want to do a tapered TL with essentially the same F3, the cabinet's depth needs to be increased to 9", and the line will become folded, ~72" long and tapered at ~15:1. Ed can certainly help you out.

        I know some people will criticize me for saying this but the Optimo TL that Tony Gee designed for the 4-ohm version of this driver is far from being an optimum design, much less a good TL. I've also attached a system response for the Optimo TL that I modeled from Tony's driver measurements and cabinet dimensions. It wasn't clear to me from Tony's information what stuffing density he used, so I modeled with three different densities and have shown the "best" results from those three densities.
        Paul

        Originally posted by Thezeek View Post
        Thanks Ed. I think Zaph's measurements would be good to use. Here they are.
        http://www.zaphaudio.com/6.5test/compare.html
        Lets try tapered.
        Opps you want Tony Gee's . Ok here it is.
        http://www.humblehomemadehifi.com/Optimo.html
        He was kind enough to send me Hi-res drawings of it today too. I could email that to you if you want.
        Attached Files

        Comment


        • #5
          Re: Transmission Line with SS 18W/8531G

          Paul thanks much for that information. Wish I had the time to sit down and mess with Martins math cad and work this stuff out. I may try just using that calculator that Keith Webb put on his site. I have a Peerless woofer I will use for that one.

          Thanks again

          M. Cote

          Comment


          • #6
            Re: Transmission Line with SS 18W/8531G

            Martin's worksheets: nothing better for the purpose

            PaulK's abilities with them: at/near the top (along with his generosity) ;)

            Zeek, it will be later this weekend before I crank it up...:o
            Mongo only pawn in game of life
            ____
            Ed

            Comment


            • #7
              Re: Transmission Line with SS 18W/8531G

              Ed, thanks mucho for the compliment.

              Zeek, I'm always happy to contribute when I have something worthwhile.
              Paul

              Originally posted by edlafontaine View Post
              Martin's worksheets: nothing better for the purpose

              PaulK's abilities with them: at/near the top (along with his generosity) ;)

              Zeek, it will be later this weekend before I crank it up...:o

              Comment


              • #8
                Re: Transmission Line with SS 18W/8531G



                Zeek & all,

                The above plot is for a tapered TL with the following parameters:
                15:1 taper
                7.5" x 9.0" @ the closed end above the 18W
                The center of the 18W is 12" from the closed end
                Total length is 80"; the open end is 7.5" x 0.6"
                The stuffing is just under a pound distributed within the first half of the line
                The response is very similar to that of the ML enclosure by Paul; it does however include ripple (+/- 1 1/2 dB) which is a characteristic of a TL
                This alignment runs out of excursion (6.5 mm) at about 30 watts & ~103 dB output

                There remain things to work out with this:

                Placement of the tweeter wrg the woofer, above or below?
                From that, the desired height of the tweeter
                The finished configuration of the enclosure, placement of the x-over, etc.
                Mongo only pawn in game of life
                ____
                Ed

                Comment


                • #9
                  Re: Transmission Line with SS 18W/8531G

                  Looks quite good, Ed. Increasing the stuffing density and/or length of stuffing would reduce the ripples some, as would shortening the line a bit but increasing the taper ratio (while keeping an eye on the terminus air velocity so it doesn't exceed a "safe' value). The latter would not sacrifice F3 any as long as the same line volume was maintained. Martin has often stated that as long as the ripple magnitude is not more than +/- 2 mm, he's happy since room effects will likely cause larger deviations anyway.

                  Now would be a good time to note a mistake I recently discovered I (and others I found out) have been making when using Martin's software. In the driver excursion graph the Y-axis is calibrated in mm RMS. Drivers' Xmax specs are in peak mm. To properly use this excursion graph, we need to multiply the driver's rated Xmax by 0.707 to convert it to RMS. For example, an Xmax rating of 6.5 mm peak, would be indicated as ~4.6 mm RMS on Martin's excursion graph. Many designers work with Xmax plus 15% in their designs, however, for a maximum safe excursion.
                  Paul

                  Originally posted by edlafontaine View Post


                  Zeek & all,

                  The above plot is for a tapered TL with the following parameters:
                  15:1 taper
                  7.5" x 9.0" @ the closed end above the 18W
                  The center of the 18W is 12" from the closed end
                  Total length is 80"; the open end is 7.5" x 0.6"
                  The stuffing is just under a pound distributed within the first half of the line
                  The response is very similar to that of the ML enclosure by Paul; it does however include ripple (+/- 1 1/2 dB) which is a characteristic of a TL
                  This alignment runs out of excursion (6.5 mm) at about 30 watts & ~103 dB output

                  There remain things to work out with this:

                  Placement of the tweeter wrg the woofer, above or below?
                  From that, the desired height of the tweeter
                  The finished configuration of the enclosure, placement of the x-over, etc.

                  Comment


                  • #10
                    Re: Transmission Line with SS 18W/8531G

                    Paul,

                    Thanks for the mention of Peak vs. RMS excursion. I was unaware of that point.
                    The option of increasing taper ratio exists. I went back to the sim and found for 30 W input the Terminus Air Velocity was ~0.005 m/sec, where a max of 0.03 is recommended.

                    I think it is time for thezeek to guide us for what he wants to see next.

                    This exercise has interest fro me as well. I have a single 18W/8531 atm...:rolleyes:
                    Mongo only pawn in game of life
                    ____
                    Ed

                    Comment


                    • #11
                      Re: Transmission Line with SS 18W/8531G

                      Ed, there's another way to configure a tapered TL. It's probably best to call it a compound TL, however, but it does minimize the necessary cabinet volume a bit for a specific F3, and it allows a more aggressive taper to be used which further reduces ripple magnitude. For a given line length, don't taper the first part of the line, say the first 25-35%, then put all of the taper in the remaining part. In a given cabinet this line will end up shorter in overall length but with a larger taper in the back end of the line, you'll end up with the same system tuning frequency. I have a scanned jpg of such a cabinet and I'll try to attach it here but it is rather "large". If I'm not successful, I'll send it to you by direct email.
                      Paul


                      Originally posted by edlafontaine View Post
                      Paul,

                      Thanks for the mention of Peak vs. RMS excursion. I was unaware of that point.
                      The option of increasing taper ratio exists. I went back to the sim and found for 30 W input the Terminus Air Velocity was ~0.005 m/sec, where a max of 0.03 is recommended.

                      I think it is time for thezeek to guide us for what he wants to see next.

                      This exercise has interest fro me as well. I have a single 18W/8531 atm...:rolleyes:

                      Comment


                      • #12
                        Re: Here's a cabinet drawing for a compound TL

                        Okay, I've re-sized this so I'm able to attach it.
                        Paul

                        Edit: I forgot to mention that you have to model this configuration with the Sections worksheet after you make a drawing to work from.
                        Paul
                        Attached Files

                        Comment


                        • #13
                          Re: Transmission Line with SS 18W/8531G

                          Interesting guys. What tweeter were you all thinking about using. I have a XT25TG30 and a B&G PDR 3.
                          I would be up to build any of the 3 put forth here.
                          How about a series crossover?

                          Comment


                          • #14
                            Re: Transmission Line with SS 18W/8531G

                            Interesting, yes.

                            I have a pair of XT25TG30's on the way, along with other equally interesting options. I need one more 18W8531G.

                            Keep in mind, these sim's are offered as indicators of what is available to you. Fine tuning to your tastes and room requirements remain to occur.

                            Don't hesitate to express your wishes.

                            I'll do a sim based on Paul's compound TL sketch, with a little more effort put into smoothing the response.

                            My bias is for a bass response which falls slightly from the ~150 Hz region. I reason that room gain will offset this. The net effect is to provide usable response just a little bit lower. I am mindful of the compromise in output. Horses for courses.

                            I can't offer any x-over solution.
                            Mongo only pawn in game of life
                            ____
                            Ed

                            Comment


                            • #15
                              Re: Beat you to it, Ed.

                              I modeled a compound tapered TL for the 8531 and offer it FWIW. The cabinet I modeled has internal dimensions of 7.5"W x 8.5"D x 38"H, and as a 2-way with the tweeter above the 8531, I modeled with the 8531's center 9" below the top (measured internally). The single-fold line ends up ~65" long, with its first 13" (the top 13" of the cabinet) not tapered, being the full 7.5" x 8.5". From there the line is folded once and tapers at ~20:1 for the rest of its ~42", ending up at 7.5"W x 7/16"D. I would make the terminus be 3.75"W x 7/8"D, however, to avoid a really narrow slot. I modeled with 0.4 ohms assumed in series with the 8531 and a stuffing density of 0.9 lb/cu.ft., with the stuffing located in the first 32" of the line's length. I have attached the system response curve.

                              Special note for Zeek: Ed and I have different opinions of how the response curve should roll off as you can see from my response curve and the one that Ed describes and will eventually display. This difference is in personal taste and doesn't necessarily imply either being superior or inferior to the other.
                              Paul

                              Originally posted by edlafontaine View Post
                              Interesting, yes.

                              I have a pair of XT25TG30's on the way, along with other equally interesting options. I need one more 18W8531G.

                              Keep in mind, these sim's are offered as indicators of what is available to you. Fine tuning to your tastes and room requirements remain to occur.

                              Don't hesitate to express your wishes.

                              I'll do a sim based on Paul's compound TL sketch, with a little more effort put into smoothing the response.

                              My bias is for a bass response which falls slightly from the ~150 Hz region. I reason that room gain will offset this. The net effect is to provide usable response just a little bit lower. I am mindful of the compromise in output. Horses for courses.

                              I can't offer any x-over solution.
                              Attached Files

                              Comment

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